I've seen a number of posts that reference this issue and typically most people suggest to do the following:
1. Log on to the Microsoft Dynamics CRM 4.0 Web client as an administrator.
2. Click Settings , click Administration , and then click Security Roles .
3. Double-click the security role that you use.
4. On the Business Management tab, set the Read privilege of the User Settings entity at least to the Business Unit level.
5. Click Save and Close.
6. try to run the report
I recently saw an issue where this didn't work. What had caused the error was the uninstall of the CRM SSRS Data Connector. This uninstall did something to the SSRS Data Source that all of the CRM reports were using. This was confirmed by changing the way the authentication was configured. If a user was hardcoded into the Data Connector then everything would work, but all reports were run as that user. If the Data Connect was set to Windows Credentials then the CRM_CalendarType error would appear (that parameter could vary). Then if "Credentials Supplied by the User running the report" was used, an unauthorized error would appear.
What was found was that NTML had been turned off both the CRM and SSRS web sites. But turning NTML back on everything began to work again.
Dynamic Methods Inc.